Of chemically unmodified immune globulins that are plasmaprotein components, chemically unmodified .gamma.-gobulin preparations mainly comprising IgG have been widely utilized for prevention and treatment of various infectious diseases. The chemically unmodified .gamma.-globulin has not been subjected to heat sterilization because of lack in heat stability and inclusion of a large number of antibodies to various viruses and bacteria.
However, in obtaining chemically unmodified .gamma.-globulin from a plasmaprotein fraction, it cannot be denied that impurity viruses, such as a hepatitic virus, may be incorporated into the preparations. Therefore, heat sterilization of the preparations has a great significance from the standpoint of inactivation of the impurity viruses.
The problem is that chemically unmodified .gamma.-globulin, when heated in an ordinary aqueous solution, e.g., physiological saline, becomes white turbid in a short time, resulting in substantial deactivation due to denaturation of protein.